This week I had a really cool early 1950s Supro Lap Steel guitar come in to the shop. The new owner, Jeb, had just recently picked it up cheap, and didn’t even know if it worked – because it had a vintage, screw-on type output jack, and the special cord for it was missing. In the early days of amplified music, manufacturers hadn’t quite settled on any sort of standardization for inputs and outputs, and so if you didn’t have the correct cable you were pretty much screwed. Now that we’ve pretty much settled on 6.35mm (1/4″) plugs, connecting a guitar to an amp isn’t usually a problem. Jeb wanted me to go through his Supro, make sure everything was working, and replace the vintage screw-on mic jack with a standard output jack. Seems like a simple job, right? Wrong.
Here’s what the original jack looks like – it’s a male jack, which a female cable screws on to. Not very convenient.
The original electronics looked like they were ok, but there was no way to tell until I could get it hooked up to an amp.
The first order of business was to remove the old jack. I desoldered the leads from the volume pot, then unscrewed the jack from the body:
The jack was screwed in to a brass insert, which would also have to come out, but the insert looked like it was being held in to the body with some sort of pin. Just fantastic. I had to figure a way to remove that pin before I could get the brass insert out. So much for this being an easy job.
I could see the top of the pin, which was depressed into the wood, so there was going to be no way I could just grab it and pull it out. 
How to remove this mystery pin without ruining the wood around it? After thinking for a bit, I opted to use my knob & bushing puller to ease it out. First I drilled a small hole into the top of the pin:
Then I drilled small hole into a penny, which I used as a washer for the tiny screw I had tapped into the top of the pin. I then secured the penny into the knob puller, and then slowly lifted the pin out.
Success! It turns out the pin was actually a nail that had been driven through wood and into the brass insert. My tiny screw had just barely grabbed on to enough of the nail to get a grip so I could remove it:
Now it was time to get that brass insert out of there. I removed as much of the solder off the side as I could, using my soldering iron and a solder sucker, and began to hammer it out from the inside:
It was a super tight fit, and wouldn’t pull out easily, so I went for the knob puller again. This time I screwed the original jack back into the brass insert, and lifted away!
Hooray! The end was in sight. I opted to install a new barrel jack, which wouldn’t require any modification to the body, but a barrel connector was designed to be held in place by a nut on the inside of the body, and there was no room in there for that. Since I was aiming for keeping the Supro original, I took an idea from their playbook, and opted to pin the jack in place. First I marked out and drilled a tiny hole in the side of the new jack, using the old nail hole as a locator:
Instead of using a nail, I used a screw to secure the jack into the body. This way if somebody had to replace the jack in the future, they wouldn’t have to go through the kind of headache I did to remove the original!
Finally I soldered the new jack to the controls, and presto! All I had to do was clean the pots, which were a bit scratchy, and everything worked beautifully. Best of all, the entire thing is completely reversible, so if Jeb wants to take it back to original spec it wouldn’t take much effort at all.
Now Jeb won’t have to worry about bringing a special cable to gigs. Sweet!
By the way, for those of you who have these kind of jacks, and you’d rather not modify your instrument in any way, Switchcraft makes some adaptor solutions you can see here: http://www.switchcraft.com/ProductSummary.aspx?Parent=810
